Apparatus for reproducing sound-on-film



15, 1936; D FOREST 2,064,593

APPARATUS FOR REPRODUCING SOUND-QN-FILM Filed April 4, 1955.

VINVENTOR; Lee de Fol-es) ATTORNEY.

Patented Dec. 15, 1936 UNITED STATES PATENT OFFICE APPARATUS FOR REPRODUCING SOUND-ON-FILM Application April 4, 1935, Serial No. 14,627

2 Claims.

This application is a divisional filed after grant of my application filed October 23rd, 1930, for Apparatus for reproducing sound-on-film, Serial No. 490,760, Patent Number 1,992,201, granted February 26th, 1935.

The present invention relates to improvements in apparatus for reproducing sound-on-film, one object of the invention being the provision of means whereby alternating current may be used in the exciter lamp without having any detrimental effect upon the photoelectric cell.

Still another object of this invention is the provision of a means whereby the frequency from the source of electrical supply may be multiplied or be made higher than originally, so as to reduce the alternating current hum in the exciter lamp in sound reproducing apparatus.

With the foregoing and other objects in view, which will appear as the description proceeds, the invention resides in the combination and arrangement of parts and in the details of construction hereinafter described and claimed, it being understood that changes in the precise embodiment of the invention herein disclosed can be made within the scope of what is claimed without departing from the spirit of the invention.

Referring to the drawing, the numeral 6 designates an exciter lamp having a filament l aligned with the optical system 8 and for projecting its beam through the film 9 and through a slit unit ill to a photoelectric cell i I, all of usual construction.

When alternating current is supplied to the filament of the exciter lamp, it is desirable to steady the beam of light so that fluctuations in the current will have no perceptible effect upon the photoelectric cell.

It is well known that when the filament is supplied with a 120 cycle alternating current instead of 60 cycles, that the period of cooling off between the half cycles is reduced to half that at the lower frequencies. I have therefore shown a simple frequency doubling arrangement. In this instance the filament l of the lamp 6 is connected to the secondary 19 of the transformer 20 while one terminal 2| of the alternating current supply is connected to the mid-tap 22 of the primary 23 of the transformer. The other terminal 24 of the alternating current supply C is connected through the two branches 25 and 25 to the outer ends of the primary 23 of the transformer and through the respective rectifying devices 26 and 2B. These rectifying devices are reversed so that one half of the 60 cycle current will pass through one half of the primary of the transformer and the following one half of the 60 cycle current will pass through the other half of the primary of the transformer thus producing a well known frequency doubling circuit in use with the present invention.

The rectifiers here shown may be of cuprous oxide, crystal, tung-ar or vacuum tube rectifiers or of any desirable type.

What is claimed is:

1. A combination in a sound-on-film apparatus including a single alternating current supply, an exciter lamp of the single filament type, a transformer, the primary of which is midtapped to the alternating current supply, a plurality of rectifiers connected to the end-taps of the primary of the transformer, and all of said rectifiers being connected to the alternating current supply, and the secondary of the transformer being connected to the filament of the lamp whereby the normal cycles of the alternating current supply are multiplied to produce a substantially constant glow in the lamp filament.

2. A combination as claimed in claim 1, wherein there are two rectifiers, and in which said rectifiers are reversed so that one-half of the current from the alternating current supply will,

pass through one-half of the primary, and the remaining one-half of said cycles will pass through the other one-half of the primary of the transformer, thereby producing a frequency doubling circuit.

LEE DE FOREST. 

